Sapphire is the single-crystal form of aluminum oxide (Al2O3) possessing excellent optical, mechanical, and chemical properties. For example, sapphire retains its high strength at high temperatures, has good thermal properties, excellent transparency, excellent chemical stability, possesses chip resistance, durability, scratch resistance, radiation resistance, and flexural strength at elevated temperatures.
For extreme conditions such as those found in high-temperature or harsh chemical environments, the unique properties of sapphire make at a cost-effective solution for those applications where long life and high performance are a must. Sapphire is widely used for various electronic and optical parts, test and analytical applications (e.g. NMR spectroscopy, thermo-optical temperature measurement, mass spectroscopy, biological and chemical sample analysis, sensor windows, FLIR, spectroscopy, and IR), lamps and lamp envelopes (e.g. electronic infrared countermeasures, ultraviolet sterilization, and high-intensity lamps).
Sapphire is increasingly becoming the material of choice for engineers faced with design challenges in the semiconductor manufacturing industry. For example, the properties provided by sapphire make it suitable for use in plasma containment tubes, process gas injectors, thermocouple protection assemblies, viewports and sight windows, end effectors, gas diffusion plates, substrates, and wafers.
Sapphire has a rhombohedral type structure and is a highly anisotropic material, with properties that are largely dependent on crystallographic orientation. The properties shown in the table of FIG. 4 are average values for different orientations.
Sapphire wafers are typically cut along a crystallographic axis such as the C-plane (0001) which is also referred to as the zero-degree plane, A-plane (1120) which is also referred to as the 90 degree plane, and R-plane (1102) which is 57.6 degrees from the C-plane. These various planes are depicted in FIG. 3.
C-plane sapphire substrates are used to grow III-V and II-VI compounds such as GaN for blue LED and laser diodes. In addition, C-plane sapphire is useful for infrared detector applications and optical systems.
R-plane sapphire substrates are used for the hetero-epitaxial deposition of silicon for microelectronic IC, semiconductor, microwave and pressure transducer applications. R-plane sapphire is also an excellent choice for hybrid substrates such as microwave IC's because of its high dielectric constant. In addition, when filmed with an epitaxial silicon process, high speed IC and pressure transducers can be created. R-plane sapphire is also useful in growing thallium, other superconducting components, high impedance resistors, GaAs, and provide a stable platform for carrying or bonding other materials. R-plane sapphire has been found to be approximately 4 times more resistant to polishing than C-plane sapphire.
A-plane sapphire substrates provide a uniform dielectric constant and high insulation for hybrid microelectronic applications. Further, high Tc superconductors can be grown with A-plane sapphire substrates.
While sapphire provides numerous advantages, due to sapphire's hardness and resistance to chemical attack, polishing and planarizing sapphire presents many difficulties. Hard abrasives having high removal rates are often required to provide acceptable polishing rates. However, these abrasives can scratch and damage the sapphire surface. While softer, slower acting abrasives can be used to reduce this potential for scratching and damage, the downside with such abrasives is the often unacceptable times required to achieve the desired level of surface polishing and planarization.
Given these and other deficiencies observed in the art, it would be highly desirable to develop improved abrasive slurry compositions that provide fast removal rate while still minimizing defects and scratching.